Answer:
Option A, labor unions substantially increased their membership, is the right answer.
Explanation:
Labor unions have played a significant role in the history of labor in the United States. Labor Unions existed in the U.S. as early as the late 1800's. Labor unions were formed to improve the working conditions, wages and benefits for workers in the U.S. The membership in such labor unions increased substantially during and after the Second World War.
One of the best ways to look for context clues would be looking for sourroundingwords bescribing whats happening for example if it said, she was terrified and sweting she couldnt focus. you would know that terriffed meant scared because of the surrounding words.